Communication system



Jan. 9, 1945. J. A. KRECEK ET AL 2,366,733

' COMMUNICATION SYSTEM Filed Aug. 28,1941 11 Shqeets-Sheei 1 FIG. 5

POLAR/ZED r/aa I FIG/2 FIG/3 J ,4. mmsx lNVE/VTORS' A TTORNE V FIG. 5

Jan. 9, 1945. J. A. KRECEK ET AL COMMUNICATION SYSTEM Filed Aug. 28,1941 ll Sheets-Sheet 2 \mm Qkm 3 3 33% khm F6 #8 :3 QHQWT uni. m 6m KW\QN8 235 MRMM .35 5 8 #35 $833 335 bin a; was 3 mm QR. Ra R8 R3 E .33 3582 mwm Q :3

3 'JLAKRECEK 'NVENTORS c. R. WALKER ATTORNEY Jan. 9, 1945. J. A. KRECEKET AL COMMUNICATION SYSTEM Filed Aug. 28, l94l ll Sheets-Sheet 5 'TITwMaM 35% A T TORNEV Jan. 9, 1945. J. A. KRECEK ETAL I COMMUNICATIONSYSTEM 11 Sheets-Sheet 4 Filed Aug. 28, 1941 .1 A. KRECEK" (NVfNTORS c.R. MLKER A TTORNE V Jan. 9, 1945. 'J. A, KRECEK ETAL COMMUNICATIONSYSTEM Filed Aug. 28, 1941 ll She ets-Sheet 5 bwk KR Dwk QR lax 4ATTORNEY Jan, 9, 1945.

v J. A. KRECEK ET L COMMUNICATION SYSTEM Filed Aug. 28, 1941 6 mm km wAR m i S mm .3 n M fii W ATTORNEY Jan. 9, 1945.

Filed Aug. 28, 1941 ll Sheets-Sheet 7 POLARIZED J ,4. KRECEK M/l ENTORSC R ML/(ER m-Maw 2%.

ATTORNEY J. A. KRECEK ET AL 33 COMMUNICATION SYSTEM Filed Aug. 28, 1941ll Sheets-Sheet 8 C. R. MLKER ATTORNEY Jan. 9, 1945.

I (WE/W095 J A/(RECE/f Jan. 9, 1945. J A, KRECEK ET AL 7 2,366,733

COMMUNICATION SYSTEM Filed Aug. 28, 1941 11 Sheets-Sheet 9 A 7' TORNEVJan. 9, 1945. J KRECEK ETAL 2,366,733

COMMUNICATION SYSTEM IIIIHI] I \5 1 w a r k I Filed Aug. 28, 1941 llSheets-Sheet 10 m0 awl I By C R. ML/(ER ATTORNEY 'Jan. 9, 1945. J. A.KRECEK ET AL COMMUNICATION SYSTEM 11 Sheets-Sheet 11 Filed Aug. 28, 1941A TTORNE V J. A. KRECEK c R. WALKER IN I/E N TORS any station connectedto that particular :party Patented Jan. 9, 1945 UNITED STATES OFFICE;-12;s6s,7s3 COMMUNICATION. SYSTEM "Joseph A. Ki-cock, New Rochelle,*Y., "and Charles T-R. Walker, Jersey i City, N. IL; "said 'Krecekas'signor to'Bell Telephone Lahoratories,

Incorporated, -New;York, N .Y.,Aa icorporationpf :New :York, and saidWalker assignor: to American Telephone and T elegraph Company,aecrimitation of New York 1 I Applicatioh'Augusf28, 19c -serialNo concur(Cl.:1-7i8 4) 21 Claims.

This *invention relates to an 'improved *telegraph transmissionswitchingsystem and to improved outlying subscriber station circuitsconnected to party lines extendingto a central switching center.

More particularly, this invention relates to an improved outlyingsubscriberstation circuit of the type; disclosed" in the -copendingapplication'of Bacon et -al.,Seria1N0. 383,490, filed March 15, 1941-andis-"arrangedto cooperate with the switchingsystemdisclosed in thatapplication.

In accordance with-the present invention, the outlying station circuitswitching equipment is arranged so that the same character may beemployed to select and" control both the transmitting apparatusat anygiven station and also the receiving apparatus at the same or any otherstation connected to any given party line. 1

Another object of this invention relates to an improved conditioning oractivating-arrangement which requires the reception "or two"predetermined cod combinations in succession in order to render atleasta portionof the switching equipment responsive "tosucceedingsignals 1 and co'de' combinations transmitted overthe sys tem.

Another feature of this invention relates "to a circuit arranged 'forreducing "the "effect "of fals or extraneous currentsuponthe-system'-'b*y requiring a specific pattern of 'the succession ofpredetermined code combinations interposed with other signals ofpredetermined character and duration to condition at least'certain ofthe switching equipment.

Anotherfeature of this invention relates to the use of -a singleselector for controlling two separate, distinct "and independent groupsof switching devices.

Another feature 'of this invention relates "to circuits and apparatusfor cancelling the effects of the reception of certainpredeterminedcharacters when they are followed; by. other signals or codecombinationsexcept when theyare im- The outlying station circuits andswitching equipmentshown in theabove-identified patent application"Bacon .et failed to "respond to or record messages'receiveds at thevarious sta tionsalong the party line unless" they were preceded by aswitching character designating a particular station'served bythe partyline indieating the station to-'which themessagewwas directed. Whenthemessages wer properly *ad- 'fdressedthe message would appear andonly'at th particular station'to which the-message was designated.However, in the-case of a mutilated or improperly designated oraddressed message being transmitted from-the -switching center to a*particular line, the entire message would be losthand'not recorded inany of the stations. In

accordancexwithithe present invention, the-circuits arearrangedto*causesuch messages to berecor'de'd at any one or more'or allof the stations connected to .th party line. Thus, in case a messageisdirected to the proper party line but the signal designatingthe'particular ,stationaonlthe line is. mutilated orlost, themessagewill'be received at some one or more of the stations. In .casethemessage is received atall of th stations .it .usually can be readilydetermined from .the .contextcf themessage which .onenof the stationsthe message should have .been transmitted to. .In this case the messagewill beidisregarded by all of the otherstations .but=wi-l1 be.considereda messagelfor the-station soaintended.

"In case -"itlisundesirable to record such improperly addressed messagesto all of thesta- ,tions, ,the;switchingg equipment located near or, :atthe :respective outlying stations may be so a arranged :that suchmessages are recorded only at ;one :or any :number of :the stationsconnectedsto .the line; this case, ,the more: lightly loaded orrcentrally located stations will be selected. '.When :such :messages arereceived. at these: stations; thecproper destination; may usuall-ylbezdeterminedtfromathecontext of the mesmediatelyiollowed by otherpredetermined 'sig r46 Sageandthe'messageg'retra'nsmittedito thepmpernals of special character and duration "or other specified codecombinations. I

Another object of this invention igto provide a switching-equipment at"one or moreof the Outlying. stationstor switchingcenters a party :50central *swit'chingrcenter. 'I'n: any case, the mesline for recordingallof the messages at oneor more of the stations whenthemessageis :precededby switching characters "not assigned to line,

station; .Invicase: the :des'tination of the message :cannot theproperly determined from the context of 'themessage, :the .message may:be retransmitted to the -originating station or to the sageis; notentirely lost.

Another feature of=this invention relates to an improved'reiayarrangement for cancelling the effect of the nclosure": of ertaincontacts 2 of 155 .the selecting equipment unless'theysareL=succeeded bythe closure of other specified or predeterminedcontacts of the selectingequipment.

Briefly, in accordance with th specific embodiment of this invention, aplurality of subscriber stations are associated with or connected toparty lines extending to a central switching station.

Secondary switching equipment is located at or near various outlyingstations of the party line. The secondary switching equipment may beindividual to each of the outlying stations or it may be common to anumber of outlying stations. The secondary switching equipment includesa selecting device which is permanently connected to the re-ceivingchannel of th party line and receives all of the signals transmittedfrom the central station over the party line. This selecting equipmentis provided with contacts which are selectively closed in respons to.

the reception of predetermined signals transmitted over the system.

This selecting equipment is arranged to control two separate, distinctand independent groups of switching devices or equipments. The firstgroup of switching devices is arranged to operatively associate thereceiving apparatus atqany of the stations controlled by the, particularsecondary switching equipment with the party line. The second group ofswitching devices is arranged to start the transmitting, apparatus atany of the stations controlled by the particular secondary equipment.

In'general, the receiving equipment at each of the outlying stationscomprises a telegraph receiving recorder of which the teletypewriter isa paths have been shown. One path is arranged to transmit signals fromthe switching center to each of the secondary switching centers locatedalong the party line and thence to the selected controlling thereceiving apparatus at the respectypical example. The transmittingapparatus at i each of these stations comprises message storingapparatus such as a keyboard perforator with which the attendantmaypunch or perforate a tape in accordance with the message to betransmitted. The stored signals or tape are'then inserted in a telegraphstorage or tape controlled transmitter for transmission to the centralswitching station. Transmission, however, does not immediately takeplace.

The telegraph'line extending from all of these stations to the centralswitching station comprises a full duplex telegraph channel capable oftransmitting messages simultaneously in both directions withoutinterference. This telegraph transmission system may be of any suitabletype and'include any of the low frequency ordirect current telegraphtransmission systems including grounded open wire lines, full metalliccable circuits, telegraph channels'of composited telephone and telegraphlines, channels of time division multiplex telegraph systems, telegraphchannels of low frequencyor voice frequency carrier current, telegraphchannels of high frequency carrier current and radio telegraph, channelsand any combination of these Various well understood telegraphcommunication transmission systems. These telegraph systems may includeany suitable type of terminal and intermediate repeat- I ers,regenerative repeaters and the like, as well as gain control apparatus,level compensators, compensating networks and equalizers, all othertypes of such apparatus and other apparatus sometimes employed insystems of these types. All the respective types of telegraph systemsoperate in their usual well understood manner so that all of the detailsof these systems have been shown.

tive outlying stations will be responsive to all but certainpredetermined signals transmitted from the central switching station.

As set forth in the above-identified patent application of Bacon et al.,each of the messages transmitted over the system is preceded by certaintelegraph signals or code combinations designating the particularstation to which the succeeding message is directed. Following each ofthe messages certain predetermined signals are transmitted indicatingthe completion of that message. The signals preceding each message areemployed at the central switching center todirect the message to theproper party line and at the secondary switching centers of that partyline, the same or at least certain of the same signals are employed toselectively and operatively associate the receiving equipment at thestation to which the message is directed with the party line. Thepredetermined signals following the message are employed to disestablishthe transmission paths and the operative connections employed in thetransmission of the preceding mes sage.

Consequently, the first signals transmitted over the receiving channelfrom the central-station willbe the switching characters preceding eachmessage. The switching equipment at each of the outlying secondaryswitching centers will respond to these signals and selectively causethe proper receiving equipment to be operatively associated with thereceiving channel of the party line. The reception of theseswitchingcharacters causes the selecting equipment at each of thesecondary stations to render the switching equipment for controlling thereceiving devices at In case the first signal or code combinationtransmitted over the receiving channel is not assigned to any of thestations associated with the party line, none of the receiving devicesat any of the stations will be operatively associated with the partyline and the selecting equipment will not render the switching equipmentnon-responsive to further signals transmitted over the line.

Normally followin the first directing signals transmitted over the line,a carriage return signal (any other suitable signal may be employed)isusually transmitted preceding thev message proper in order to properlyposition the carriage of the receiving device for the reception of thefollowing message. The circuits at one or more of the switching centersare arranged to respond to this carriage return signal and cause thereceiving equipment at one or more of the stations controlled by thesecondary switching centers to be operatively associated with the partyline. In

the specific embodiment of the invention shown in the drawings,connections are made so as to caus the receiv ng qu pment at all of thet ions t be iterat vely associated withthe receiving channel of theparty line under these circum.- stances. Consequently, the message willbetrans- .mitted to all of i the stations of the party line.

The reception of the carriage return signals under these circumstancescauses the switching equipment for controlling the receiving apparatusto be rendered non-responsive to any further sig- .ill

centers and cause only one or more but not all of] the receiving devicesto. be associated with the receiving channel. Ii; is also, within thescope of this invention to provide'a special receiving device for.receiving such messages. and causing the messages to be recorded onlyupon thisspew cial receiving device. H

.In the specific embodiment of this linvention shown in the drawings,the figures signal followed by anH signal is employedto indicate the endof each message.

the operative receiving equipment to. be non-responsive to furthersignalstransmitted over the receiving channel of the party line andfurther causes the switching equipmentfor controlling the receivingequipment at all of the stationsto be rendered responsive to thesucceeding signals transmitting over the receiving channel of the partyline. Consequently, the first signals preceding the neXt message whichwill be transmitted over the receiving channel of the party line willcause the proper receiving apparatus to be operatively associated withthe receiving channel.

Thereafter. the circuit will operate in the manner isimilarto thatdescribed above.

As indicated above the attendants at each of the outlying s ations willperforate the tape in accordance with the message to be transmitted tothe central switching station andthereafter insert the perforated tapein the tape controlled transmitters at each of these stations; Switchingsignals will be perforated in the tape preceding each message and afigures signal followed by.

an H signal will be perforated in the tape at the end of each message.It is to be understoo'd that suitable signals, such as letters signals,will be perforated in the tape between any of the various switchingsignals and between the switchin signals or code combinations in themessage as may be necessary to provide sufficient time for enablin theswitching apparatus to function and establish the necessary transmissionpaths.

In order to start the transmission from any of the outlying stations, itis necessary that certain predetermined code combinations and signals betransmitted from the central station over the receiving channel. Theselect ng equipment at each'of the secondary switching centers respondsto these signals and causes the switching equipment controlled therebyto start the desired one of the transmitters whereupon the message istransmitted to the central ormain transmitting center.

are started in the specific embodiment of this in- *Vention disclosedherein is briefly as follows.

Any transmission over the receiving channel from the central switchingstation is first interrupted for a short interval of time following whch a blank codeicombination is transmitted from the The reception of thefigures sig- H nal immediately followed by an H signal causes I Themanner in which the transmitters prises a code combination iii-which allfive of the significant selecting impulses are of a spacing.

character. Following the blank code combination a pause of approximately.7 of a second istransmitted from the central station... During thispause the marking condition is applied to the receiving channel of theparty line. A predetermined code combination such as thatrepresentingthe letterR is then transmitted from the central station and when thissignal isreceived it causes any transmitter which may be connected to ortransmitting overthe transmission channel to be stopped and disconnectedtherefrom. Following the letter R. signal, a second pause ofapproximately, .7 of a second is transmittedfrom the central stationfollowing which a selecting code combination is transmitted .whichewillselectively start and operativelycassociate any one of the transmitterswith the transmission channel of the party line; Following thetransmission of this selecting code combination, transmission from thethe central office will be resumed after a slight pause. i i i Thecircuits at each of the secondary switching centers are so arranged thatif. signals are received during the pause in transmission following theblank signal, the eifect of the blank signal is cancelled whereupon thecircuits are reestablished as if no blank signal had been received. Iffollowing the blank signal no further signals'are received during this.7 second .interVaL'the transmission path extending from the receivingchannel to any receiving equipment associated therewith is renderedineffective so that furthersig:

nals cannot be recorded as part of the message being received. If theletter R signal is not received within apredetermined time ofapproximately 2 to 5 seconds. the efiects of the blank signal arecancelled. If the selecting code combination is not received withinasimilar neriodof time ofv approximately 2 to 5 seconds followingv the R.signal, the circuits are restored to'their previous conditions, that is,the transmission pathbetween the receiving channel and the previouslyselected receiving apparatus is reestablished but none of thetransmitters at operative.

The circuits are so arranged that the transmission of messages over therece ving. channel may be interrupted at any sta e for the transmissionof the signals for starting. any of the transmitters and thereaftertransmission of the message resumed without adding any characters to themessage being transmitted or without deany of the stations will beleting ormutilating any of the switching or mes- Fig 1 shows the mannerin which Figs. 5

thrpugh 13, inclusive, are positioned adjacent one i another to form atypical party line circuit arcentral station. A. blank code combinationcom 75 rangement in accordance with this invention;

Fig. 2 shows the manner in which Figs. 3 and 4 are positioned adjacenteach other for showing a suitable central line station;

j Figs. 3 and 4 when positionedas shown in Fig. -2 show. in outline formthe various circuitson the central switchingstation; and i i Figs.through 13, inclusive, when arranged as shown in Fig. 1 show the detailsof the sec- .ondary switching centers and outlying stations associatedwith a typical party line designed in accordancev with this invention.

Figs. 3 and 4 show in block form the various circuits at a typicalcentral stationsimilar to that disclosed in the above-identifiedcopending patent application of Bacon et a1. and are equivalent to Figs.3 and 4'of said copending patent application. Figs. 5 through 13 arearranged to cooperate with this switching system and may be placedadjacent to Figs. 3 and 4, in which case the party. line shown in Figs.5 through 13, inclusive, is shown connected toparty line 200 comprisinga receiving channel 204 and transmitting channel205. As maybe wellunderstood by'persons skilled in the art, the party line'shown in Figs.5 and 13 rnay cooperate equally well with any of the other party lines,such as with the party lines 2M and 202 of the central switching stationshown in Fig. 3. It is also apparent that additional party lines maybeprovided each of which is provided with equipment similar to thatshown in Figs. 5 through 13. It is to be understood that all of theseparty lines do not necessarily include the same number of'stations orhave the stations arranged in the same manner or associated with thesame number of secondary switching centers. Instead, the stations andsecondary switching centers may be arranged in any manner which mayappear tube the most suitable in view of all of the factors in eachparticular case. These factors include among others geographicalselection and separation of the various stations and also the trafficrequirements of each of the stations. In general, sufiicient stationsare connected to a given party 7 line to insure that it will operate ator near its Figs. 44, 45, 53 and 54 of that application. When thesefigures are substituted for-any of the groups of figures referred toabove comprising party line circuits, they will cooperate with theswitching equipment of said copending application in the same manner asthe party linesshown described in said application. As will be readilyunderstood by those skilled in the art, the number of stations connectedto each of the lines will vary as conditions require. In addition, theapparatus at-the central switchstation, such as the transmitter startcircuits and apparatus, may be altered and changed to cooperate with thestations connected to the respective lines. I

It is deemed unnecessary to show all the details and describe thedetailed operation of this switching equipment at the central switchingstation since it operates in substantially the same manner as describedin theabove-identified copending patent application of Bacon et a1. andto which reference may. be' made for more detailed description thereof.In the following description it will be assumed that whenthe party lineshown in Figs. 5 and 13is connected to the party line 200 of Fig. 3, thecentral station equipment and circuits have been modified as required bythe number of stations connected to the line, and

. crossbar switch that the central switching equipment operatessubstantially as described in the above-identified cope'ndingapplication. Y

Normally when power is applied to the system, the relays generallyassume the position as shown in the drawings. The various motors drivingthe selecting equipment at the secondary switching centers, as well asmotors driving the ceivedeither on a receiving only teletypewriter ifthey are intended for the central switching 'st'a- V tion or on a typingreperforator if they arcintended for other stations connected to thesystem. In order to control this equipment an incomingline circuit 3!!is provided in which" the transmitting channel 265 of line2iilltermina'tes.

The tape 323 from the reperforator 3l8 controls the transmitter 32!Signals recorded in tape '323 together with the'tape transmitter 326',director SH and selector magnet 322 cause the tape transmitter 320 to be"connected through the to the proper outgoing line circuit.

Any suitable type of the crossbar switch may be employed forestablishing the connection between the transmitter 326 and the properoutgoingline circuit. The details of the crossbar switch have not beenshown in full since switches of this type are well known in the priorart and I the switch incorporated in this invention operates 'in theusual or customary manner. For a more detailed description of themechanical and electrical features of a typical switch suitable for usein this invention, reference "is madeto United States Patent 2,021,329,granted to Reynolds November 19, 1935. M 1

The outgoing line circuit is provided with two These channels' may beoperated simultaneously to record different messages' When the firstchannel is busy recording another 'message, a,secon d message will bereceived from the transmitting distributor over the second channel. Atyping re- ,perforator is associated with each of these channels. Thus,in Fig. 3, 3M represents the typing reperforator associated with thefirst channel of the outgoing line circuit 3H5, while 315 represents thetyping reperforator associated with the second channel of the outgoingline circuit 3|6.

Assuming that bothohannels areidle and that a message is directed tosome station connected tofull duplex line 200, the message willbetransmitted over the first channel of. the outgoing line circuit 316and recorded .by the typing. repertorator 3!! in a tape 324. Tape 324will .thencontrol the transmitter. 312, causing the message to betransmitted over the receiving channel 204 of transmission system 208 tothe desired station.

In addition to thetransmitters M2 and 313 connected to the receivingchannel 204 of line we, the transmitter controlcircuit 3H0 andassociatedsignal code transmitter 31 l'are also connected to the outgoing orreceiving channel 204 of the line 200. The transmitter start'circuit-3l0and the associated transmitter} I I are provided toselectively start thetransmitters located at the stations served by thisparty line and' toopera tively associate them. one at a time with the transmitting channelof fullduplex line 260. I The other full duplex lines 29],132 are similarly provided with terminal equipment at the central switching station.In addition. arrangements are made so that the second channel of" theoutgoing line circuit connected to line 20.2 may be d-isasso'ciated withline 202 and employedto receive other messages which are improperlytransmitted or for some -reason improperly directed to the correctstation. i

Line 203 is provided with similar terminal equipment'at. the central.station, except that" i the transmitter start circuit and its associatedtransmitter are not provided because only one station is connected toline 293. Consequently, there is no need for selectively starting thetransmitter fromthe central station.

- In addition, two local keyboard perforators M8 and 438 are provided atthe centralswitching station for perforating tape inraccordance withsignalstobe transmitted to other stations of the. system. This tapecontrols the associated transmitters flfl and 44d. These transmittersare in turn provided wwith directors MI and M1,. re-

spectively', to enable them to 'be connected tothe desired-linesextending torthe proper station. Two intercept circuits lfilli and 49flare provided for receiving messages which are improperly switched orimproperly transmitted over the sys tem. Arrangements are also; providedfor direct ing messages intended forany one of thestatio'ns which may beshut down or inoperative due to trouble to either of theseinterceptcircuits where the messages are recorded by the respective printingreperforators 458 and H8. The tape.

perforated by the typingreperforator 458 is employed to controltransmitter 460. With the aid of theassociateddirector 46! thistransmitter may be connected to anyof the outgoing line circuitsundercontrol of'perforationsin the tape.

An interlocking circuit is provided betweemeach of the director circuitsto prevent more than one of the director circuits setting up aconnection secondary switching center shown in Fig. 7.

. Five outlying stations are shown in Figs. l2 and 13.Theseoutlyingstations are controlled by the secondary switching centersshown in Figs. 8

and 9.. l

i l "It is to be understood that any number of switching centers maybeassociated. Withany party line and that any number of stations may beassociated with any given secondary switching centers. 1 However,traffic studies indicate. that a maximum of five outlying stationscontrolled by. one switching center and a maximum often stationsconnected to a given party line and controlled from. one to tensecondary switchingcenters would adequatelymeet all of the traffic.requirements of any party line likely to. be encountered in commercial.telegraph net works. It. is to be understood, however, that there are nobasic limitations: to these numbers. of stations or switching. centers.which. may be associated with any given party line nor are there anylimitations regarding the specific number shown in the embodiment ofthis invention herein described. It will be re'adily understood by thoseskilled in the art that the switching centers and outlying stations. maybev arranged in. any desirable mannerin accordance withoperatingytraffic and geographical considerations. s

It is assumed that in the embodiment of this invention described hereinthe stations lshownin Fig. 10 are designated by the letters A, B and C,station. shown in Fig; 11 by the letter D, those in Fig. lZ'by E, F andG, and the stations in Fig. 13 by the letters X and Y. Thus when anymessage transmitted over the receiving channel from the centralswitchingstation is preceded by any of these letters; the message will berecorded at the proper station.

The receiving channel 2940f the party line 236.

extends through theline windings ofline relays 883,103 and 603 of therespective receiving selectors 91H, l0! and 601 at the secondaryswitching through the crossbar switch at a given instant of time. Thecircuits" are arranged, however, so that once the circuit is establishedthrough the crossbar switchby one di'rector, other director circuits mayestablish other connections through the switch withoutdisturbingtheconnections already established; Busy-te t arrangements are alsoprovided to indicate whether either or both of the channels of theoutgoinglinecircuits are busy, so that .a director willbeunable toconnect its associated transmitter to a busy channel of an outgoing.line circuit.

In. the specific embodiment shown in Figs. 5

centers. The receiving channel 204 also extends through the linewindings of the repeating relays 9E3; 984, 985, 183 and $83 and 6M.at'the respec tive switching centers. All of these relays follow allofthe signals transmitted from the central switching station overthereceiving channel 204 1 of party line 2&0. Repeatinglrelays 683, 684,183,

throughv 13,. inclusive, three: secondary switching centers. are. shown.connected to the party line 20!]. Figs. 5 and. 6.- showthe detailsofthe. sec? ondaryswitching center rjnost remote fromthecentral.switching station... Fig. 7 shows thefdeatails of anintermediate switching center while Figs. 8- and 9 show in. detail thecircuitsuand switching equipment rof theswitching center adjacent thecentraltswitching. station.

Three outlying stationsare shown in .Fig. 10 to be associated with andcontrolled by the secondary switching centershown-in Figs. 5 and 6.

The details: of the equipment and the circuits of aisingle outlying.stationrare shown in F'igmll.

. and. 2,154,547, granted toWalker April 18, 1939, "which patents are.hereby made a. part of this application as if fully included herein. Thevarious contacts controlled by the selectors at each of the secondaryswitching centers are momen tarily operated each time the proper codecombination or character is received by the selector ,magnet. However,as described hereinafter.

closure of these contactsis effective to control the switching equipmentat each of these stations only under certain circumstances. a 1

The station shown in Fig. 11 is controlled'by the r Selection of anoutlying station and the transmission of amessage to the selectedstation "As pointed out above, each message is preceded by certainsignificant switching characters each designating the station to whichthe following message is directed or addressed. Assuming the firstmessage transmitted from the transmitters 3I2 or 3I3 over the receivingchannel 204 of the party line 200 is intended for station A, that is,

the left-hand station shown in Fig. 10; this message will be preceded bythe letter A. I When the letter A signal is transmitted by one of thetrans mitters 3I2 or 3 I3 over the receiving channel 204, it will causerelays 903, I03 and 603 to respond and repeat this character to therespective selecting magnets 902, I02 and 602. These selecting mag netswill in turn cause the selecting equipment in each of these stationswhich is controlled by them to close the respective contacts 9I0, H and6 I0. The closure of contacts 9I0 completes a circuit for the operationof relay 929 from ground through the momentarily closed contacts 9I0 thesecond right-hand break contacts of relay 904 to battery through thewinding of relay929. Re-

its outer operated contacts to battery through the winding of relay 904.Relay 904 operates and interrupts the circuits between contacts of theselecting mechanism SM and the switching relays at stations shown inFig. 9 which control the receiving devices associated with this controlstation. In other words, further operation of any of these contacts isineffective to operate any of the switching relays at this point.Consequently,

none of the stations controlled from the secondary switching centershown in Figs. 8 and 9 will receive any of the message signals followingthis A signal; It is to be noted that the selector magnet 902 willfollow all of the signals transmitted over the receiving channel of theparty line and cause the corresponding contacts to momentarily close.However, this selector when responding to these signals will not alterthe switching circuits until certain predetermined signals have beenreceived as 'will be described hereinafter.

Similarly relay 193 at the intermediate secondary switching center willrespond to the letter A signal and repeat it to the selector magnet 102.This magnet causes selector mechanism 'IOI to momentarily close contactsH0 and complete a circuit for the operation of relay I29. Relay I29 inoperating completes a circuit for maintaining itself operated undercontrol of relay I31 and also completes a circuit for the operation ofrelay I04. Relay I04 in operating disconnects the contacts controlled byselector 'IIJI from the switching relays which control the receivingapparatus located at the station shown in Fig. 11. Consequently, themessage will not be recorded by this receiving apparatus.

The relay 603 also responds to the letter A signal transmitted from thecentral switching station and repeats this signalcombination to theselector magnet I302. Selector magnet 602 in responding to this codecombination causes contacts flowing in a circuit from battery throughthe;

winding of relay 630 to ground through the lefthand break contacts ofrelay 604 and the operated contacts 6I0. Relay 630 in operatingcompletes a circuit for maintaining itself operated from battery throughits winding and left-hand inner operated contacts and the left-handinner break contacts of relay 631 to ground through the rightehand inneroperated contacts of relay,630.

Relay 630 in operating completes a circuit for the operation of relay604'from battery through the winding of-re1ay 604 to ground through theat this station.

Relay 630 in operating also completes a circuit for lighting lamp 650from ground through the right-hand outer break contacts of relay 68I andthe right-hand outer operated contacts of relay 630 to battery throughlamp 650. Lamp 650 in lighting indicates to the attendant that thestation associated therewith, namely, station A shown in Fig. 10, isoperatively associated with or connected to the receiving channel of theparty line.

Operation of relay 630 also connects the ar-' mature of the repeatingrelay 684 to line I 02!.

Consequently, when relay 684 followsthe message signals of the followingmessage it will repeat these signals over the conductor I02I to stationA. The transmissionpath from the armature of relay 684 may be tracedfrom they contacts and armature of relay 684, through the outerleft-hand break contacts of relay 68I through the outer left-handoperated contacts of relay 630, conductor I02I tostation A and linewinding of relay I022 to ground. At station A relay I022 will followthese signals and repeat them to magnet I023. This magnet will cause thesignals to be recorded by the receiving device I024 at station A. Thusthe signals following the letter A signal will all be received by thereceiving device I024 at station A. Following the transmission of the Asignal from one or the other of transmitters 3| 2 and 3I3 from. thecentral switching station one or more letters signals may be transmittedto provide sufiicient time for the operation of the various relays andcircuits described above. Normally a carriage return signal, a line'feedsignal and another letters signal will be transmitted it is pointed outabove, circuits will remain in this condition so long as this message isbeing transmitted to the station. It'should be noted that the same codecombinations which were initially used to control the switching relaysand circuits may be transmitted during the message without changing theconnections or the switching ap- 'paratus. In the specific example underconsideration, the letter A whichwas used to establish arcane thetransmission pathut o station A may be transmitted a number or times.during the message without further aifecting the circuits or any of thesecondary switching stations. Similarly; characters designating the.other stations connected .to the party line may be transmittedduring thetransmission atthe message without at.- fecting the circuits: at or toany of these stag ti'ons.

At the end of this message a figures signal will be transmittedfollowed: by an H signal. It should be noted that should :a figuressignal, .be transmitted during the message which is followed 645.It'should be notedthatthe only possible circuits through the'l'owervwinding' of relay 546 at thisttime are the circuits which extendthrough either the figures contacts 625, blank .contacts 621, and the5H=combination 6H. Theoperation of the circuit wh'en the-particular codecombination is a fig-ures code combination is substantially the same asdescribed abovewnen the first figures of the figures signal will becancelled.

The operation of the circuits under these conditionsis as: follows: Uponthe transmission of a figures signal contacts 625 of the selector Billwill momentarily close. Momentary closure car-these contacts completesthe circuit for .the operation of/relay G'tifrom ground, through theclosed contacts filifigright-hand winding, of relay 645: to batterythrough the lower winding of relay 54.6. As indicated current flowingthrough theilower winding of relay 546,, which is'a. polarized relay, is'in such a direction as to maintain its armature in: its right handposition :as shown :inthe drawings. Relay 6 ,35 in operating completes acircuit for" maintaining itself operated from" battery through itsleft-hand winding, the left-hand onterxbreak contacts of relay 631.,theuleft-hand and right-hand outer operated contacts of relay 64 5 toground through the right-hand contact and armature of relay546.Operation of relay M5 also completes a circuit fromgroundthroug'h theuniversal contacts 626 and right-handinner operated contacts of relay645 to battery through the upper winding of relay 546. Current flowingin this circuit tends to cause the armature of relay 546 to be operatedto its left-hand position. However, this current produces an effect uponrelay 546 which is weaker than. the. efiiect produced upon relay v546 bythe current flowing through the lower winding of this relay.Consequently, relay 546 is maintained-in the position shown on thedrawings atthis time.

Contacts 626 are closed once for each code combination received by; theselector mechanism BM. These contacts, howeverydo not close until: afterthe other contacts close. if the particular code combination received isone that normally controls any of these other contacts. In addition thecontact 625 opens before any of the other-contacts open. Consequently,the circuit "through the lowerwinding. .of relay 546 is closed first andmaintained closed for ashort interval 1 time'may be traced from groundthrough the operated universal contacts 626, the right-hand l. inneroperated contacts of relay 645 to battery,

through the upper winding of relay 546. Current flowing in this pathwill cause the armature,

of relay 546 to be operated toits left-hand position and. interrupt thelocking circuit of relay code combination was transmitted over the sys:tem. If the particular code combination happens to be a blank codecombination, the circuitwill operate as describedhereinafter. If theparticular' code combination is an Hcomb ination, the circuit willoperate to disconnect the receiving equipment at station A;

Assuming that the code combination following the figures codecombination is neither-an I-I code combination nor a blank combination,the oper ation'of relay Ho as described, above interrupts the lockingcircuit of relay 645 and permits this relay to release. Rel-ease'ofrelay 64'5 returns the circuit to its preyiousco-ndition and cancels theeffectot the reception of the figures code combination in so far astheswitching equipment of the secondary switching center shown in Figs:

5 and 6 is concerned, Thereafteras many upper case characters includingthe H character or code combination may be transmitted over the systemandl recorded by the receiving device shown at station A withoutaffecting the switch- Q ingequipment or the transmission circuits eXtendingto station A. i

The selecting equipment at the intermediate secondaryswitching stationssuch as shown in Figs? responds in asimilar manner to the transmission,of theiigure-signal followed by any signa'l otherthan a blank signal oran H signal. Relay 245 will be operated and then later released bytheoperation of relay H6.

Likewisere-lay 9ll5 will' beeperated at the first secondary switchingcenter in response to the reception of the figures signal. Thereafterrelay Ski-will be-o-pera-tedto its left-hand position in responsetothefollowing code combination which under the assumed conditionisneither an H signal norablank signal. The operation of relay llfi'interrupts the locking circuitof relay 945 and thispermits this relayto release and cancel the effect of the figures signal upon theswitching: circuits. i

It should be noted that the receiving apparatus conneotedltothereceiving channel receives and properly responds to the figuressignal but the sheets of th-i-s signal upon the receiving apparatusisnot cancelled as described above with reterence tothe switchingequipment. The effect or'the figures signal upon the receiving.apparatus is cancelled only in -response to a letters signal andsometimes in response to a character spacing or other predeterminedsignal.

Assuming now that a codecombination immediately following the figurescode combination is an H code combination; whenthis code combinaat thistimecompletes a circuit through the lower winding of relay 546 formaintaining its armature in theposition shown. This circuit maybe tracedfrom ground through the closed contactsfill, the left-hand inneroperated contactsof relay 645; winding of relay 631 to battery throughthe lower Winding of relay 548. Relay 631 operates due to currentfiowing'through this circuit and relay 54B is maintained in theposiinthe position shown where it maintains the loeking circuit forrelay 645 and also for relay Relay 631 when operated completes a circuitfor maintaining itself operated from battery through the lower windingof relay 546, winding of relay 631, the right-hand inner operatedcontacts of relay 631, the right-hand and left-hand outer operatedcontacts of relay 645 to ground through the right-hand contact andarmature of relay 546.

Relay 631 in operating interrupts the locking circuit of relay 636 andthus permits this relay to release. The operation of relay 63'! howevermaintains a circuit through the winding of relay 664 closed and thusmaintains relay 664 operated as long as relay 63? remains operated. Theoperation of relay 631 also interrupts the locking circuit of thefigures relay 645 and thus permits this relay to release. Release ofrelay 645 interrupts both the operating and the locking circuit of relay637 and permits this relay to release. The release of relays 637 and 645interrupt the holding circuit of relay 664 and permits this relay torelease. switching center shown in Figs. 5 and 6 is returned to thesame. condition as it was in beginning and is thus ready to respond to adirecting character which will be transmitted preceding the next messagetransmitted over the receiving channel 204 of partly linev 200.

The circuits at the other secondary switching centers shown in Fig. '7and Figs. 8 and 9 respond in a similar manner and first cause theoperation of relays 745 and 131, the release of relays 129,

Thus the circuit at. the secondary 145, 131, 104 in the order named andthus restore the circuit to its original condition. In a similar mannerthe circuits at theother secondary switching center shown in Figs. 8 and9 are also restored to their initial condition in response to thefigures code combination immediately followed by an H code combinationtransmitted at i the endof the message which was transmitted to stationA.

Assume now that the switching characters preceding the next messagewhich has been routed by the switching equipment at the centralswitching station to this line will be preceded by a first characterwhich will not be the letter A, B, C,

I D, E; F, G, X or Y. Under these circumstances -mitted over thereceiving channel 204. Consequently, none ofthe switching relayscontrolled by these contacts will operate to connect any of thereceiving devices at any of the receiving stations to the receivingchannel. -As pointed out above, following the first signals transmittedover the receiving channel one or more letter signals are usuallytransmitted in order to provide suf- ,ficient time for the switchingcircuits to function.

Following the transmission of the letter'signals a carriage returnsignal and a linefeed signal followed by a letters signal are usually,trans mitted in order to properly position the carriage.

at the receiving instrument at the station to which the message isdirected. If none ofthe switching contacts controlled by the selectorsat the various stations have been operated when the carriage returnsignal is transmitted over the system, the selecting equipment at eachof the secondary switching centers will respond to this signal and causethe respective contacts 628, I28 and 928 to momentarily closeandcomplete circuits for the operation of relay 648 atthe most remotesecondary switching center, relay 148 at the intermediate switchingcenter, relay 948 at the first switching center. The circuit for theoperation of relay 648may be traced from ground through the closedcontacts 628, the inner lefthand break contacts of relay 604 to batterythrough the winding of relay 648. Relay 648 in operating completes acircuit for maintaining itself operated from battery through the windingof relay 648, the right-hand outer break contacts of relay 63'! toground through the right-hand operatedcontacts of relay 648.- As shownin the drawings the operation of relay 648 will complete circuits forthe operation of relays 630, GM and 632 because all of the straps 615are shown provided between the contacts of relay 648 and the windings ofthese relays. Consequently,.the operation of relay 648 will cause eachof these relays to operate which in turn will cause the receivingequipment at each of the stations, A, B and C to be operativelyassociated with the receiving channel 284. Consequently, all of thesestations will receive the following message transmitted from thecentral. switching station.

In a similar manner relay .148 completes a circuit for the operation ofrelay 133 and the relay 133 in turn operatively associates the receivingequipment at the station shown in Fig.

-11 with the receiving channel 264.

Likewise the operation of relay 948 at the first secondary switchingcenter completes circuits for the operation of relays 934, 935, 936, 943and 944, the operation of which relays operatively associate thereceiving equipment of all of receiving channel of the party line.

The operation ofall of these switching relays at each of the secondaryswitching centers completes the circuits for. maintaining themselvesoperated under control of the respective relays 631, 13'! and 931. Themessage following the carriage return signal will then be recorded bythe receiving apparatus of all of the stations associated with the partyline. In general this message will be intended for some one of thestations connected to the party line and the attendants at therespective station can usually readily determine from the context of themessage the particular station for which it is intended andthe messagereceived in the other stations, will be ignored and the messageconsidered a proper one at the proper station. In case a message isintended for some. other sta 'tion than the one of the stations ofthisparty line, the attendants at one or more of the stations may beassigned the duty of transmitting the message either back to the centralswitching not all of the stations connected to any given party line. Inorder to accomplish this thestraps the stations shown in Figs. 12 and 13with the signal followed by the H signal will be transmitted to thecircuits ateach of the secondary switching centers which will respond tothese signals in the same manner as describedabove and restore thecircuits and equipment to its original idle or normal condition.

It is also possible to broadcast any message to all stations of anygiven party line by transmitting a carriage return signal or, any otherspecifically designated code combination, which will cause the relays648, 148 and 948 or relays similar to these relays to operate at each ofthe secondary switching centers. If these relays are thus operatedinstead of the: relays individual to each of the stations, they willcause all of the individual relays to be operated as described above andcause the message to be recorded at each of thestations served by theparty line. Similarly by suitable connecting contacts on these relaysand the individual relays described above any group of the stationsassociated with the respective party line may be selected for thesimultaneous transmission of messages relay 604 to other contactscontrolled by the being transmitted from the central switching.

selector mechanism as desired. The contacts of these relays would beconnected to the windings of the desired individual relays as describedabove.

Starting a transmitter At any time during transmission ofa message fromthe central station to any of the outlying stations it is possible tointerrupt the transmission then in progress and send transmitter startsignals over the receiving channel 204 of the party line 208.

As pointed out above, the attendants at each of the outlying stationswill perforate the tape in accordance with the messages to betransmitted and insert the perforated tapes in the transmitter.Thereafter the message will be transmitted under control of the centralstation. Normally, the operator at the central switching .station'willcontrol a special circuit so that it will send out a group of. signalsinterspersed with pauses of predetermined duration constituting afollowed by an H signal will be perforated in the tape at the end of themessage. The perforated tape is then inserted in the transmitter. Theinsertion of the tape in the transmitter causes contacts [M5 to close..The closure of these contacts merely partially prepares a circuit forthe operation of relay lll3.

Assume further that a message is in progress of station to the receivingequipment shownat station B. Under these circumstances, if the operatordesires to start the transmitter at station D she will operate certainswitches or other apparatus at the switching station to initiate theoperation of the transmitter start circuit and equipment whereupon thetransmission in progress over the receiving channel 204 from the centralstation to station B is first interrupted by stopping the transmitter atthe central switching station. After the transmission has been stoppedfor a short interval of time of the order of a half of a second or asecond, a blank code combinationis transmittedfromthe transmitter startcircuit over the system. In the blank code combination the fivesignificant selectin impulses are all spacing. This blank codecombination when transmitted over the receiving channel 284 is receivedby the receiving apparatus at station E.

This apparatus however in. responding to this code combination does notprint any character nor does it advance the printingposition a characterspace or respond in any other manner to this blank code combination. i l

The selector magnets 682, 102 and 982 also respond to this blank codecombination and cause their respective selector equipments tomomentarily close the respective blank contacts 621, 121 and 921. Theclosure of contacts 621 completes a circuit for the operation of relay541 from battery through the lower winding of relay 555, winding ofrelay 541 to ground through the closed contacts of 621. The operation ofrelay 541 completes the circuit for the operation of relay 518 whichrelay in turn completes the circuit for maintaining its-elf operatedfrom battery through through the lower windingof relay 546 and re-.

mains completed through the lower winding of this relay until after theuniversal contacts 526 lopen, relay 545 is maintained in the positionunderstoodof course, that switching or directing signals will beperforated in the tape prior to the messageand that the figures signalimmediately shown. Later when contacts 621 open relay 541 will releaseand interrupt the circuit through the upper winding of relay 511.

Normally relay 5111's maintained .in the position shown bycurrentfiowing in a circuit from battery through its upper winding,lower contacts of key 59! to ground through the left-hand break contactsof relay 518. A circuit is also completed through the lower winding ofrelay of relay 511. The armature of relay 511 does not.

